Conference minotr::security_advisory

139.0. "Information Only: CERT CA-97.11, libXt" by MINOTR::NOBLE (Your Data, Your Job...Protect Both) Thu May 08 1997 08:51

             
    The Digital Corporate Information Security Group has received the
    following external security notice.  At the time of writing this
    document, patches(binary kits) are in progress and final testing is
    expected to begin soon.  Digital will provide an internal user notice
    of the completion/availability of the patches via a CISG Security
    Advisory.
    
    This third party notice is being provided as information only.  No
    security action is required at this time.  Nor is any recommendation 
    being made with regards the solution(s) identified.
    
    Should you happen to be using the third party software impacted by
    this notice, please use due discretion before implementing any or all
    of the solution(s) identified.
      
                                  -=<>=-
    
=============================================================================
CERT* Advisory CA-97.11
Original issue date: May 1, 1997
Last revised: --

Topic: Vulnerability in libXt
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There have been discussions on public mailing lists about buffer overflows in
the Xt library of the X Windowing System made freely available by The Open
Group (and previously by the now-defunct X Consortium). The specific problem
outlined in those discussions was a buffer overflow condition in the Xt
library, and the file xc/lib/Xt/Error.c. Exploitation scripts were made
available.

Since then (the latter half of 1996), The Open Group has extensively reviewed
the source code for the entire distribution to address the potential for
further buffer overflow conditions. These conditions can make it possible for
a local user to execute arbitrary instructions as a privileged user without
authorization.

The programs that pose a potential threat to sites are those programs that
have been built from source code prior to X11 Release 6.3 and have setuid or
setgid bits set. Some third-party vendors distribute derivatives of the X
Window System, and if you use a distribution that includes X tools that have
setuid or setgid bits set, you may be vulnerable as well.

The CERT/CC team recommends upgrading to X11 Release 6.3 or installing a 
patch from your vendor. If you cannot do one of these, then as a last resort 
we recommend that you remove the setuid or setgid bits from any executable 
files contained in your distribution of X; this may have an adverse effect on
some system operations.

We will update this advisory as we receive additional information.
Please check advisory files regularly for updates that relate to your site.

- -----------------------------------------------------------------------------

I.   Description

     There have been discussions on public mailing lists about buffer
     overflows in the Xt library of the X Windowing System made freely
     available by The Open Group (and previously by the now-defunct X
     Consortium). During these discussions, exploitation scripts were made
     available for some platforms.**

     The specific problem outlined in those discussions was a buffer overflow
     condition in the Xt library and the file xc/lib/Xt/Error.c. It was
     possible for a user to execute arbitrary instructions as a privileged
     user using a program built by this distribution with setuid or setgid
     bits set.

     Note that in this case a root compromise was only possible when
     programs built from this distribution (e.g., xterm) were setuid
     root.

     Since then The Open Group has extensively reviewed the source code for
     the entire distribution to address the potential for further buffer
     overflow condition.

     If you use a distribution of the X Windowing System earlier than
     X11 Release 6.3 that you downloaded and compiled yourself, we
     encourage you to take the steps outlined in either Section IV A or C.

     If you use third-party vendor-supplied distributions of the X
     Windowing System containing setuid root programs, we encourage
     you to take the steps outlined in Sections IV B or C.

     ** Note: Discussions of this specific instance of the vulnerability
        appeared on mailing lists during the second half of 1996. Exploitation
        scripts were made public at that time.

II.  Impact

     Platforms that have X applications built with the setuid or setgid bits
     set may be vulnerable to buffer overflow conditions. These conditions can
     make it possible for a local user to execute arbitrary instructions as a
     privileged user without authorization. Access to an account on the system
     is necessary for exploitation.


III. Finding Potentially Vulnerable Distributions

     A.  For Sites That Download and Build Their Own Distributions

     As discussed earlier, the programs that pose a potential threat to sites
     are those programs that have been built from source code, prior to X11
     Release 6.3 and have setuid or setgid bits set.

     Sites that have downloaded the X source code from the X Consortium
     should be able to identify such programs by looking in the directory
     hierarchy defined by the "ProjectRoot" constant described in the
     xc/config/cf/site.def file in the source code distribution. The
     default is /usr/X11R6.3. The X11R6.3 Installation Guide states:

        "ProjectRoot
              The destination where X will be installed.  This variable
              needs to be set before you build, as some programs that read
              files at run-time have the installation directory compiled
              in to them.  Assuming you have set the variable to some value
              /path, files will be installed into /path/bin,
              /path/include/X11, /path/lib, and /path/man."


     B.  For Vendor-Supplied Distributions

     Some third-party vendors distribute derivatives of the X Window
     System. If you use a distribution that includes X tools that have
     setuid or setgid bits set, then you may need to apply Solution B or C
     in Section IV.

     If you use a distribution that does not have setuid or setgid bits
     enabled on any X tools, then you do not need to take any of the steps
     listed below.

     Below is a list of vendors who have provided information about this
     problem. If your vendor's name is not on this list and you need
     clarification, you should check directly with your vendor.


IV.  Solution

     If any X tools that you are using are potentially vulnerable (see Section
     III), we encourage you to take one of the following steps. If the setuid
     or setgid bits are not enabled on any of the tools in your distribution,
     you do not need to take any of the steps listed below.

     For distributions that were built directly from the source code
     supplied by The Open Group (and previously by the X Consortium), we
     encourage you to apply either Solutions A or C. For vendor-supplied
     distributions, we encourage you to apply either Solutions B or C.


     A.  Upgrade to X11 Release 6.3

         If you download and build your own distributions directly from the
         source code, we encourage you to install the latest version, X11
         Release 6.3. The source code can be obtained from

                ftp://ftp.x.org/pub/R6.3/tars/xc-1.tar.gz
                ftp://ftp.x.org/pub/R6.3/tars/xc-2.tar.gz
                ftp://ftp.x.org/pub/R6.3/tars/xc-3.tar.gz

         Note that these distributions are very large. The compressed
         files consume about 40M of disk space. The uncompressed tar files
         consume about 150M of disk space.


     B.  Install a patch from your vendor

         Below is a list of vendors who have provided information about
         this problem. Details are in Appendix A of this advisory; we will
         update the appendix as we receive more information. If your
         vendor's name is not on this list, the CERT/CC did not hear from
         that vendor. Please contact your vendor directly.

            Berkeley Software Design, Inc. (BSDI)
            Digital Equipment Corporation (DEC)
            FreeBSD, Inc.
            Hewlett-Packard Company
            IBM Corporation
            NEC Corporation
            NeXT Software, Inc.
            The Open Group (formerly OSF/X Consortium)
            The Santa Cruz Operation, Inc. (SCO)
            Sun Microsystems, Inc.


     C.  Remove the setuid bit from affected programs

         If you are unable to apply Solutions A or B, then as a last resort
         we recommend removing the setuid or setgid bits from the
         executable files in your distribution of X.

         Note that this may have an adverse effect on some system
         operations.  For instance, on some systems the xlock program needs
         to have the setuid bit enabled so that the shadow password file
         can be read to unlock the screen. By removing the setuid bit from
         this program, you remove the ability of the xlock program to read
         the shadow password file. This means that particular version of
         the xlock program should not be used at all, or it should be
         killed from another terminal when necessary.


...........................................................................

Appendix A - Vendor Information

Below is a list of the vendors who have provided information for this
advisory. We will update this appendix as we receive additional information.
If you do not see your vendor's name, the CERT/CC did not hear from that
vendor. Please contact the vendor directly.


Berkeley Software Design, Inc. (BSDI)
=====================================
  We released a patch for this for the 2.1 BSD/OS release,
  and it's already fixed in our current release.


Digital Equipment Corporation (DEC)
===================================
At the time of writing this document, patches(binary kits) are in progress and
final testing is expected to begin soon.  Digital will provide notice of the
completion/availability of the patches through AES services (DIA, DSNlink
FLASH) and be available from your normal Digital Support channel.


FreeBSD, Inc.
=============
We're aware of the problem and are trying to correct it with a new release of
the Xt library.


Hewlett-Packard Company
=======================
         For HP-UX, Install the applicable patches:

       PHSS_10167       9.X   X11R5/Motif1.2  Runtime
       PHSS_10168       9.X   X11R5/Motif1.2  Development

       PHSS_9809        10.0X/10.10  X11R5/Motif1.2  Runtime
       PHSS_9810        10.0X/10.10  X11R5/Motif1.2  Development

       PHSS_10688       10.20 X11R5/Motif1.2  Runtime
       PHSS_9813        10.20 X11R5/Motif1.2  Development

       PHSS_10789       10.20 X11R6/Motif1.2  Runtime
       PHSS_9815        10.20 X11R6/Motif1.2  Development


        Apply the library patches and relink any suid/sgid programs
        that are linked with the archived version of libXt.


IBM Corporation
===============
  See the appropriate release below to determine your action.


  AIX 3.2
  -------
    Apply the following fix to your system:

       APAR - IX61784,IX67047,IX66713 (PTF - U445908,U447740)

    To determine if you have this PTF on your system, run the following
    command:

       lslpp -lB U445908 U447740


  AIX 4.1
  -------
    Apply the following fix to your system:

        APAR - IX61031 IX66736 IX66449

    To determine if you have this APAR on your system, run the following
    command:


       instfix -ik IX61031 IX66736 IX66449

    Or run the following command:

       lslpp -h X11.base.lib

    Your version of X11.base.lib should be 4.1.5.2 or later.


  AIX 4.2
  -------
    Apply the following fix to your system:

        APAR - IX66824 IX66352

    To determine if you have this APAR on your system, run the following
    command:

       instfix -ik IX66824 IX66352

    Or run the following command:

       lslpp -h X11.base.lib

    Your version of X11.base.lib should be 4.2.1.0 or later.


  To Order
  --------
    APARs may be ordered using Electronic Fix Distribution (via FixDist)
    or from the IBM Support Center.  For more information on FixDist,
    reference URL:

       http://service.software.ibm.com/aixsupport/


    or send e-mail to [email protected] with a subject of "FixDist".


  IBM and AIX are registered trademarks of International Business Machines
  Corporation.


NEC Corporation
===============
   EWS-UX/V(Rel4.2) R7.x - R10.x   vulnerable
   EWS-UX/V(Rel4.2MP) R10.x        vulnerable
   UP-UX/V(Rel4.2MP) R5.x - R7.x   vulnerable
   UX/4800 R11.x - current         vulnerable

   Patches for this vulnerability are in progress.
   For further information, please contact by e-mail:
      [email protected]


NeXT Software, Inc.
===================
X-Windows is not part of any NextStep or OpenStep release.  We are not
vulnerable to this problem.


The Open Group (formerly OSF/X Consortium)
================================
Not vulnerable.


The Santa Cruz Operation, Inc. (SCO)
====================================
We are investigating this problem and will provide updated
information for this advisory when it becomes available.


Sun Microsystems, Inc.
======================
We are investigating.


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The CERT Coordination Center staff thanks Kaleb Keithley of The Open Group
for helping us understand the nature and scope of this problem.
- -----------------------------------------------------------------------------

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Copyright 1997 Carnegie Mellon University
This material may be reproduced and distributed without permission provided
it is used for noncommercial purposes and the copyright statement is
included.

* Registered U.S. Patent and Trademark Office.
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